POS1485 SEMIQUANTITATIVE ASSESSMENT OF SYNOVIAL INFLAMMATION ON US-GUIDED SYNOVIAL TISSUE BIOPSIES OF SYSTEMIC LUPUS ERYTHEMATOSUS COMPARED TO OTHER CONNECTIVE TISSUE DISEASES AND RHEUMATOID ARTHRITIS
Authors: C. DI Mario, L. Petricca, A. Paglionico, V. Varriano, M. R. Gigante, S. Perniola, D. Bruno, B. Tolusso, S. Alivernini, E. Gremese
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic Lupus Erythematosus patients might experience the development of arthritis clinically resembling other forms of chronic joint inflammation. However, to date, no systematic analysis of the histological composition of synovitis was performed in SLE patients. <h3>Objectives</h3> To dissect the inflammation degree and the histological composition of synovial tissue of SLE patients compared with other Connective Tissue Disorders (CTD) and naive to treatment Rheumatoid Arthritis (RA). <h3>Methods</h3> Seventy-five patients with connective tissue diseases [n=30 SLE, n=13 Sjogren Syndrome (SS), n=19 Undifferentiated Connective Tissue Disease (UCTD), n=13 other CTD] were included in the study. Thirty-four naive to treatment RA patients were included as comparison. Each patient underwent ultrasound-guided minimally invasive synovial tissue biopsy at the study entry. Each synovial tissue sample was processed for H&amp;E staining for the Krenn Synovitis Score (KSS) assessment by a pathologist blinded to clinical characteristics [1]. This evaluation was implemented with the additional assessment of lymphocytes and plasmacells presence, and with the assessment of the microanatomical organization in terms of inflammatory aggregates presence. <h3>Results</h3> Considering the whole cohort, SLE patients showed comparable synovial inflammation in terms of KSS compared to SS and other CTD (p&gt;0.05 for both). However, synovial tissue of SLE patients showed significantly milder inflammation when compared to naive to treatment RA (p=0.002) and more severe compared to UCTD (p=0.009), mainly in terms of inflammatory infiltrate (p=0.015). Moreover, among SLE cohort, patients with Rhupus showed higher KSS compared to SS (p=0.03), mainly for synovial hyperplasia (p=0.016) and comparable synovial inflammation than naive to treatment RA (p&gt;0.05). Considering the composition of the inflammatory infiltrate, synovial tissue of SLE patients was enriched of lymphocytes compared to synovial tissue of SS (p=0.0028), UCTD (p=0.014) and other CTD (p=0.018), similarly than synovial tissue of naive to treatment RA (p&gt;0.05). Moreover, SLE patients showed, at synovial tissue level, higher rate of plasmacells compared to SS (p=0.038) despite significantly lower than naive to treatment RA (p=0.007). Interestingly, among the whole SLE cohort, synovial tissue of Rhupus patients was enriched of plasmacells compared to synovial tissue of SLE patients (p=0.04). Finally, considering the microanatomical organization of synovial inflammation, SLE patients showed lower rate of synovial aggregates compared to naive to treatment RA (p=0.03), the latter having similar aggregate rate compared to Rhupus patients (p=0.23). <h3>Conclusion</h3> Synovitis in SLE patients, despite milder than in naive to treatment RA, is characterized by more severe features compared to other CTD. In particular, Rhupus patients show a degree of synovial inflammation in terms of KSS and microanatomical organization comparable to naive to treatment RA, supporting the need to dissect pathogenetic pathways driving this clinical phenotype. <h3>Reference</h3> [1]Alivernini S, et al. Arthritis &amp; Rheumatology 2021 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.